Bacteria is found virtually everywhere and is responsible for a significant amount of disease and infection. Killing and/or eliminating these microorganisms is desirable to reduce exposure and risk of disease.
Bacteria in many environments are present in high concentrations and have developed self preservation mechanisms and, therefore, are extremely difficult to remove and/or eradicate. They can exist in planktonic, spore and biofilm forms.
In a biofilm, bacteria interact with surfaces and form surface colonies which adhere to a surface and continue to grow. The bacteria produce exopolysaccharide (EPS) and/or extracellularpolysaccharide (ECPS) macromolecules that keep them attached to the surface and form a protective barrier effective against many forms of attack. Protection most likely can be attributed to the small diameter of the flow channels in the matrix, which restricts the size of molecules that can transport to the underlying bacteria, and consumption of biocides through interactions with portions of the EPS/ECPS macromolecular matrix.
Bacteria often form spores, which provide additional resistance to eradication efforts. In this form, the bacteria create a hard, non-permeable protein/polysaccharide shell around themselves which prevents attack by materials that are harmful to the bacteria.
Additionally, bacteria in biofilm- or spore forms are down-regulated (sessile) and not actively dividing. This makes them resistant to attack by a large group of antibiotics and antimicrobials, which attack the bacteria during the active parts of their lifecycle, e.g., cell division.
Due to the protection afforded by a macromolecular matrix (biofilm) or shell (spore) and their down-regulated state, bacteria in biofilm- and spore states are very difficult to treat. The types of biocides and antimicrobials effective in treating bacteria in this form are strongly acidic, oxidizing, and toxic, often involving halogen atoms, oxygen atoms, or both. Common examples include concentrated bleach, phenolics, strong mineral acids (e.g., HCl), hydrogen peroxide and the like. Commonly, large dosages of such chemicals are allowed to contact the biofilm or spore for extended amounts of time (up to 24 hours in some circumstances), which makes them impractical for many applications.
Recently developed formulations intended for use in connection with compromised animal/human tissue can solvate a biofilm matrix so that still-living bacteria can be rinsed or otherwise removed from infected tissue; the concentrations of active ingredients in these formulations are too low to effectively kill the bacteria, thus making them ill suited for use as disinfecting agents. More recently, solutions that can disrupt the macromolecular matrix, or bypass and/or disable the defenses inherent in these matrices, allowing lethal doses of antimicrobial ingredients in the solutions to access and kill the bacteria in their biofilm and sessile states have been described; unlike the aforementioned formulations, these solutions can be used as disinfectants.
Most water filtration is accomplished using filters made of materials such as paper, fiber, and synthetic fibers. Unclean, bacteria-laden water is passed through a membrane having a controlled pore size, typically on the order of ˜0.20 to ˜0.45 μm. These membranes are effective at keeping bacteria from passing through them into a clean water reservoir, but they do not weaken, disable or kill the bacteria. This latter characteristics make such membranes susceptible to bacterial growth, thereby increasing the risks of contamination with biofilms and spore-forming bacteria and reduced flow rates due to clogging.
Silver-loaded ceramic filters use the antimicrobial properties of silver to kill bacteria as they pass through a porous ceramic substrate. To achieve high efficacy, flow rates must be kept low. Further, these filters have a high propensity for clogging. Finally, silver ions are not particularly efficacious in debilitating and killing bacteria in biofilm- and spore forms.
Devices and articles can be provided with coatings that include antimicrobials such as cationic compounds (e.g., quaternary ammonia compounds), silver and copper compounds, and peptides. These coatings are limited in their efficacy against resistant forms of bacteria and have very thin regions of effective antimicrobial effect. These types of coatings are generally designed to prevent surface attachment of bacteria rather than to disinfect.
Certain eluting devices and articles are designed to slowly release anti-bacterial compounds when exposed to moisture. These solids typically been impregnated by antimicrobial agents which, over time, work their way to the surface and are released. The concentrations of solutions eluted from these devices and articles, as well as the efficacy of the employed antimicrobial agents against resistant forms of microbes, are low. The utility of such devices and articles is further reduced in situations where a liquid is to pass through the device due to more rapid depletion of the antimicrobial agent(s).
A solid material capable of preventing bacterial growth, and preferably killing bacteria coming into contact with or close proximity to the solid material, remains desirable. Such a solid preferably can be useful in a variety of forms including, but not limited to, filters, eluting devices, and coatings.